Microfluidic chips including microchannels contribute a lot to developments in the fields of cell biology, chemical engineering and medical engineering by enabling small-scale experiments. Many parts of microfluidic chips are being developed, including mixers, valves and sorters. Among them, the valve is studied a lot since it allows free flow of a fluid in the chip and control of the sample amount.
A few schemes have been presented thus far. The most commonly employed method is to attach a thin elastic polymer membrane between two chips and blocking the channel of the upper or lower chip using external pressure. However, to insert the membrane, the upper and lower chips have to be separated completely and this process is complicated in control of the thin membrane.
There is another method that uses a hydrogel. In this method, fluid flow is controlled by controlling the motion of the material which is sensitive to electric field or pH in the channel. However, this method is very difficult to realize and is inapplicable to long-term use for a sensitive sample since it can be affected by the electric field or pH.